Andrew, Great thoughts and I think you make a good point about hearing a truer, more plaintive delivery from many of the Canadian singers. Another Canadian artist who sings "unambitiously" is Diana Krall. Not so sure where k.d. laing fits in. I kind of think that really is her natural voice - she seems to pull it off so effortlessly. Some rare singers are gifted with both emotional verity and technical virtuosity.
Joni also said in the interview "I haven't heard a girl singer who wasn't trying way too hard in 20 years." and "I'd rather have it be emotionally correct than have some great vocal athlete tear it up on it." I enjoy both kinds of singers but the ones who are "emotionally correct" are usually the ones who impress me the most long term. Kakki